Light intensity and sowing depth on the emergence and development of weeds

: Background: Weeds are one of the ecological factors that affect the agricultural economy permanently. Thus, understanding the weed emergence and development is essential in decision making for management strategies. Objective: This study aimed to evaluate the effect of different sowing depths and light intensities on the emergence and development of the weed species Euphorbia heterophylla and Desmodium tortuosum under field conditions. Methods: Each species consisted of an experiment carried out in a completely randomized design with four replications. Treatments were arranged in a 6 × 4 factorial scheme, with six sowing depths (0.5, 1.0, 2.0, 4.0, 8.0, and 12.0 cm) associated with four light intensities (100, 70, 50, and 30% of the solar light intensity) obtained with shading screens. Seedling emergence capacity was evaluated daily to obtain the percentage of emergence and the emergence rate index (ERI). Plant height, time to floral induction, plant dry matter during flowering were also evaluated. Results: Seedlings of E. heterophylla emerged under all solar radiation conditions and sowing up to 12.0 cm deep, while seedlings of D. tortuosum showed no emergence only at 12.0 cm deep with light intensities below 70%. The 100% solar radiation condition provided higher total and daily dry matter accumulation in E. heterophylla plants, while D. tortuosum plants showed higher values for both variables under 70 and 50% incidence of solar radiation. Conclusions: The full sunlight condition provided the best development of E. heterophylla plants. Different levels of lightness and sowing depths interfere the emergence and the development of D. tortuosum plants.